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<span class="token comment"># 执行的命令主体</span>
<span class="token function">ls</span>
<span class="token builtin class-name">echo</span> <span class="token string">&quot;hello world&quot;</span>
</code></pre></div><ul><li><p>#!/bin/bash ：指定脚本要使用的 Shell  类型为 Bash</p></li> <li><p>ls、echo： 脚本文件的内容，表明我们执行  hello.sh  脚本时会列举出当前目录的文件列表并且会向控制台打印 `hello world</p></li></ul> <p>执行方式为<code>.hello.zsh</code></p> <h2 id="二、种类"><a href="#二、种类" class="header-anchor">#</a> 二、种类</h2> <p><code>Linux</code> 的 <code>Shell</code> 种类众多，只要能给用户提供命令行环境的程序，常见的有：</p> <ul><li><p>Bourne Shell（sh），是目前所有 Shell 的祖先，被安装在几乎所有发源于 Unix 的操作系统上</p></li> <li><p>Bourne Again shell（bash） ，是 sh 的一个进阶版本，比 sh 更优秀， bash 是目前大多数 Linux 发行版以及 macOS 操作系统的默认 Shell</p></li> <li><p>C Shell（csh） ，它的语法类似 C 语言</p></li> <li><p>TENEX C Shell（tcsh） ，它是 csh 的优化版本</p></li> <li><p>Korn shell（ksh） ，一般在收费的 Unix 版本上比较多见</p></li> <li><p>Z Shell（zsh） ，它是一种比较新近的 Shell ，集 bash 、 ksh 和 tcsh 各家之大成</p></li></ul> <p><img src="https://static.vue-js.com/8e739440-0883-11ec-a752-75723a64e8f5.png" alt=""></p> <p>关于 <code>Shell</code> 的几个常见命令：</p> <ul><li>ls：查看文件</li> <li>cd：切换工作目录</li> <li>pwd：显示用户当前目录</li> <li>mkdir：创建目录</li> <li>cp：拷贝</li> <li>rm：删除</li> <li>mv：移动</li> <li>du：显示目录所占用的磁盘空间</li></ul> <h2 id="三、命令"><a href="#三、命令" class="header-anchor">#</a> 三、命令</h2> <p><code>Shell</code> 并不是简单的堆砌命令，我们还可以在 <code>Shell</code> 中编程，这和使用 <code>C++</code>、<code>C#</code>、<code>Java</code>、<code>Python</code> 等常见的编程语言并没有什么两样。</p> <p>Shell 虽然没有 C++、Java、Python 等强大，但也支持了基本的编程元素，例如：</p> <ul><li>if...else 选择结构，case...in 开关语句，for、while、until 循环；</li> <li>变量、数组、字符串、注释、加减乘除、逻辑运算等概念；</li> <li>函数，包括用户自定义的函数和内置函数（例如 printf、export、eval 等）</li></ul> <p>下面以<code>bash</code>为例简单了解一下<code>shell</code>的基本使用</p> <h3 id="变量"><a href="#变量" class="header-anchor">#</a> 变量</h3> <p><code>Bash</code> 没有数据类型的概念，所有的变量值都是字符串，可以保存一个数字、一个字符、一个字符串等等</p> <p>同时无需提前声明变量，给变量赋值会直接创建变量</p> <p>访问变量的语法形式为：<code>${var}</code> 和 <code>$var</code> 。</p> <p>变量名外面的花括号是可选的，加不加都行，加花括号是为了帮助解释器识别变量的边界，所以推荐加花括号。</p> <div class="language-bash extra-class"><pre class="language-bash"><code><span class="token assign-left variable">word</span><span class="token operator">=</span><span class="token string">&quot;hello&quot;</span>
<span class="token builtin class-name">echo</span> <span class="token variable">${word}</span>
<span class="token comment"># Output: hello</span>
</code></pre></div><h3 id="条件控制"><a href="#条件控制" class="header-anchor">#</a> 条件控制</h3> <p>跟其它程序设计语言一样，Bash 中的条件语句让我们可以决定一个操作是否被执行。结果取决于一个包在<code>[[ ]]</code>里的表达式</p> <p>跟其他语言一样，使用<code>if...else</code>进行表达，如果中括号里的表达式为真，那么<code>then</code>和<code>fi</code>之间的代码会被执行，如果则<code>else</code>和<code>fi</code>之间的代码会被执行</p> <div class="language-shell extra-class"><pre class="language-shell"><code><span class="token keyword">if</span> <span class="token punctuation">[</span><span class="token punctuation">[</span> <span class="token number">2</span> -ne <span class="token number">1</span> <span class="token punctuation">]</span><span class="token punctuation">]</span><span class="token punctuation">;</span> <span class="token keyword">then</span>
  <span class="token builtin class-name">echo</span> <span class="token string">&quot;true&quot;</span>
<span class="token keyword">else</span>
  <span class="token builtin class-name">echo</span> <span class="token string">&quot;false&quot;</span>
<span class="token keyword">fi</span>
<span class="token comment"># Output: true</span>
</code></pre></div><p><code>fi</code>标志着条件代码块的结束</p> <h3 id="函数"><a href="#函数" class="header-anchor">#</a> 函数</h3> <p>bash 函数定义语法如下：</p> <div class="language-bash extra-class"><pre class="language-bash"><code><span class="token punctuation">[</span> <span class="token keyword">function</span> <span class="token punctuation">]</span> funname <span class="token punctuation">[</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">]</span> <span class="token punctuation">{</span>
    action<span class="token punctuation">;</span>
    <span class="token punctuation">[</span>return int<span class="token punctuation">;</span><span class="token punctuation">]</span>
<span class="token punctuation">}</span>
</code></pre></div><ul><li>函数定义时，function 关键字可有可无</li> <li>函数返回值 - return 返回函数返回值，返回值类型只能为整数（0-255）。如果不加 return 语句，shell 默认将以最后一条命令的运行结果，作为函数返回值</li> <li>函数返回值在调用该函数后通过 $?  来获得</li> <li>所有函数在使用前必须定义。这意味着必须将函数放在脚本开始部分，直至 shell 解释器首次发现它时，才可以使用。调用函数仅使用其函数名即可</li></ul> <h2 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h2> <ul><li>http://c.biancheng.net/view/706.html</li> <li>https://juejin.cn/post/6930013333454061575</li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/14/2021, 10:12:35 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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